Employees at retail chain Spotlight say they were forced to attend a morning meeting every day for at least a decade without being paid for it.

Three former employees told Checkpoint today that attendance at Spotlight Christchurch's 8.45am meeting - a quarter of an hour before shifts began - was compulsory, but they were not allowed to include it in their timesheets, so were never paid for it.

Checkpoint has been contacted by dozens of employees from businesses and public organisations across New Zealand after it was revealed on Friday that retail chain Smiths City underpaid minimum wage workers for at least 15 years, by also expecting them to attend an unpaid 8.45am daily meeting.

The Employment Court has ordered Smiths City to work out how much it owed affected employees, and back-pay them by 8 August this year.

Former Spotlight employee Anne-Marie Brittenden worked for minimum wage at the Christchurch store for five years until late 2016.

"[At the meetings] we were given instructions on specials, behaviours, and expectations," she said.

"The number of staff who went were counted, and your names were written down."

A full-time worker on the minimum wage would miss out on about $800 a year if they attended a daily 15-minute meeting without pay.

That would take their total remuneration below the minimum wage threshold, making the practice illegal.

Spotlight general manager Chris Moore declined to be interviewed today, but in a statement through the company's PR firm, said the company had launched an internal investigation into the unpaid meetings.

"It is an absolute priority that our staff are paid fairly and for all hours worked, so if this is not the case then we need to address that immediately," Mr Moore said.

He denied the meetings were compulsory.

"It has always been optional for staff members to attend and, while it is encouraged, not attending will not lead to disciplinary action," he said.

"In response to the Smiths City recent ruling, we sent out a directive to all Spotlight NZ regional managers last week to cease all meetings outside of rostered hours (regardless of the fact they are voluntary)."

But a current employee confirmed the store held a morning meeting today, and staff would not be paid for it.

Mr Moore said any Spotlight employee who had been underpaid should contact the business.

"I encourage anyone else who feels they were not given an option to attend out-of-hours meetings, to come forward and speak to myself or their store manager.

"We will manage any future instances on a case-by-case basis," he said.

Retail giant Briscoes has also been accused of forcing staff to attend unpaid morning meetings but group general manager Rod Duke said all staff were paid for morning meetings.

"Is it possible there's been a slip-up? Probably," he said,

"But there's been no slip-up with the meetings, and I'm half-way through checking [whether staff were paid for] the end of evening cash-up," Mr Duke said.

Any Briscoes staff who were found to have been underpaid could expect to be reimbursed "immediately", he said.

Unions and the government both believe the practice is widespread.

They warned businesses to make sure they were paying all staff for all hours worked.

Workplace relations and safety minister Iain Lees-Galloway said he was concerned about the number of businesses being accused of underpaying minimum wage workers.

"This practice is not acceptable, and [I hope] they will quickly change their business practices to get themselves in line with the law," Mr Lees-Galloway said.